STRUCTURE OF HAIR. 



141 



due ; whilst the medullary substance is composed of an aggregation of very 

 large cells, which seem not to possess any fluid contents in the part of the 

 hair which is completely formed. The structure of the feather of Birds is 

 precisely analogous ; the cortical horny tube existing alone in the quill ; but 

 being filled with a cellular medulla in the stem of the feather itself. In the 

 hair of the Mouse and other small Rodents, we see the horny tube crossed 

 at intervals by partitions, which are sometimes complete, sometimes only par- 

 tial ; these are the walls of the single or double line of cells, of which the 

 medullary substance is made up. In the Sable, we sometimes meet with 

 hairs, in which the medulla is made up of rounded cells ; whilst the cortical 

 substance is composed of imbricated Epidermic scales (Fig. 35, B). In some 

 instances, however, there is scarcely any medulla to be traced ; whilst in 

 other animals, as the Musk-deer (Fig. 35, A), the entire hair seems to be made 

 up of it. 



[Fig. 36. 



B. 



A, hair of Musk-Deer 

 consisting almost entirely 

 of polygonal cells; B, hair 

 of Sable, showing large 

 rounded cells in its inte- 

 rior, covered by imbrica- 

 ted scales, or flattened 

 cells. 



Bulb of a small black hair, from the scrotum, seen 

 in section, a. Basement membrane of the follicle, b. 

 Layer of epidermic cells resting upon it, and becoming 

 more scaly as they approach c, a layer of imbricated 

 cells, forming the outer lamina, or cortex, of the hair. 

 These imbricated cells are seen more flattened and 

 compressed, the higher they are traced on the bulb. 

 AVithin the cortex is the proper substance of the hair, 

 consisting at the base, where it rests on the base- 

 ment membrane, of small angular cells scarcely larger 

 than their nuclei. At d. these cells are more bulky, 

 and the bulb consequently thicker; there is also pig- 

 ment developed in many of them more or less abun- 

 dantly. Above d, they assume a decidedly fibrous cha- 

 racter, and become condensed, e. A mass of cells in 

 the axis of the hair, much loaded with pigment.] 



167. In the Human hair, the representation of the cortical sheath of the hair 

 of other animals is found in a thin transparent horny film ; which is composed 

 of flattened cells or scales, arranged in an imbricated manner, their edges 

 (Fig. 36) forming delicate lines upon the surface of the hair, which are some- 

 times transverse, sometimes oblique, and sometimes apparently spiral (Fig. 

 37, A). Within this, we find a cylinder of fibrous texture ; which forms the 



